The present invention relates to a metallic damping body, and, more particularly, to a shape-memory alloy damping body for shock-type stresses and/or periodically changing stresses.
Journal ZwF 84 (1989) 4, pages 215 to 217, P. Tautzenberger, "Dampfungsvermogen von Formgedachtnis-Legierungen [English translation, Damping Capacity of Shape-memory Alloys]" mentions the comparatively high damping capacity of shape-memory alloys, compared with other metals, especially in the state of a martensitic microstructure. The damping capacity is, however, not permanently high, but changes as a function of various influencing parameters such as the microstructure state, namely martensitic or austenitic; operating temperature (damping is at an optimum high level around the martensite start temperature); alternating strain level (at high alternating strains, the martensitic microstructure shows very effective damping over a wide temperature range); static base load; and mechanical and thermal pretreatment, and the aging state.
In connection with a static prestress of a damping body consisting of a shape-memory alloy and the effect thereof on the damping behavior, it is stated that, by application of a static prestress, preferred martensite variants are formed which reduce the size of the highly mobile interfaces in the material, whereby a decrease in damping capacity results. The applicant herein is able to confirm this observation only partially or only under certain conditions. For example, it has not been possible to accomplish the high damping values when the damping body was made in the form of bearing shells or other flat damping substrates.
It is an object of the invention to improve the aforementioned type of metallic damping body consisting of a shape-memory alloy such that a high damping effect is achieved even a high mechanical stress of the damping body.
This object has been achieved according to the present invention in that the shape-memory alloy has an austenitic microstructure state at an operating temperature of the damping body, and a sufficiently high mechanical prestress is applied to the damping body such that the working damping range is within a pseudoelastic strain range of the shape-memory alloy selected, which strain range starts just below a proportionality limit in a stress/strain diagram of the shape-memory alloy and continues above a proportionality region of the stress/strain diagram.
Due to the use of mechanically highly pre-stressed shape-memory alloys in the austenitic state, the pseudoelastic range of this alloy type or of this state of microstructure associated with very pronounced hysteresis is utilized for damping purposes.
Advantageously, a porous structure, or a structure containing voids of the damping body, is provided in compressively stressed damping bodies in order to obtain fully effective damping even with such damping members. This is based on the surprising discovery that a reduction in damping, observable under compressive stress, of a solid damping body is at least partially caused by the occurrence of multi-axial stress states due to impeded transverse extension within the damping body, and a resultant reduction in internal interfacial friction. Due to the porosity or distribution of voids in the interior of the damping body in accordance with the present invention, the occurrence of multi-axial stress states is prevented, so that there is no interference with the mutual mobility of the internal interfaces and the latter can therefore rub on one another.